Today, many forms of medium are used to store data. Examples of data storage medium include a compact disc (CD) such as CD read-only memory (CD-ROM), CD recordable (CD-R), CD rewritable (CD-RW) and CD read only memory (CD-ROM), and a digital versatile disc (DVD) such as DVD read-only-memory (DVD-ROM), DVD random-access-memory (DVD-RAM) and DVD read-write (DVD-RW). Typically, a laser beam is used to write on and to read a material stack of these data storage mediums. Information may be stored in a sequential, planar fashion in these material stacks. Existing technologies utilize an outward spiraling, sequentially ordered stream of data blocks written or molded onto the top of the lands or the bottom of the grooves of the media. In many of these applications, the medium of choice is a chalcogenide, phase-change media where the information content is written as a sequence of varying length or position dependant spots where the reflectance of the media reflects the written states of the medium.
The material stack may include a thin-film of material such as a phase-change chalcogenide alloy material to store information or material with similar variable resistance properties that indicates the states of the material as it was written. In particular, a low-energy electron stream may be used to change the state of the phase-change material, amorphous or crystalline, to write information in the data storage medium. To recover the information from the data storage medium, a low-energy, lower current electron stream may be used to sense the resistance of the phase-change material. The voltage required to project a small diameter spot of electrons in the form of a focused beam, e-beam, is in the range of 100 to 100,000 volts.
However, non-contact sensing of the resistance state of a region of phase-change material in the presence of voltages greater than a few volts, typically greater than 10-volts, might require circuit isolation and this is typically accomplished at significantly increased expense. To sense small variations in the resistance at these anode voltages, and at low currents with current low-voltage silicon circuits such as a complementary metal-oxide semiconductor (CMOS) can be difficult and expensive.
Therefore, a need exists for a robust, non-contact, low-cost means to determine a resistance state of a rapidly sensed sequence of phase-change material regions in a data storage layer within a material stack.